Neural Plasticity has been around for a long time, but not widely researched. Neural Plasticity is defined by Berlucchi and Buchtel (2009, p.307) as “changes in neural organization which may account for various forms of behavioral modifiability, either short-lasting or enduring, including maturation, adaptation to a mutable environment, specific and unspecific kinds of learning, and compensatory adjustments in response to functional losses from aging or brain damage.” According to Berlucchi (2002, p.305) , it was first Ernesto Lugaro, in 1906 in Italian and 1909 in English, with his publication of a treatise of Pyschiatry in which he used the terms “psychic plasticity” and “plasticity of neurons.” Eugenio Tanzi, Ernesto Lugaro’s teacher, felt that the more neural connections are used, the closer they become (Berlucchi, 2002). The establishment of neural plasticity allowed for many abstract ideas about learning and memory find a meaning in the physical realm of science.
Neural plasticity is one of the most important discoveries in the realm of the brain because it allows for more surgery to be done as well as allows for a more comprehensive understanding of how the functions of the brain are specified. The implications of this notion affected the study of learning and adaption. Cajal is the first to say that this type of action takes place in regards to learning because he believed that new neural connections must take place for learning to occur (Berlucchi & Buchtel, 2009). William James is known for attributing this phenomenon to habituation which basically means that, the more we use certain neurons and their connections, the stronger those connections become (Berlucchi & Buchtel, 2009). James (1890) found that nerve tissue was important to memory formation in that it enabled, by changing, to allow for the memory of that stimulus to be recreated but not to the full extent in which it was experienced. This allowed for the concept of memories to be better realized and when two processes have neurons firing simultaneously then there is a better chance of an association to be formed (Berlucchi & Buchtel, 2009). Cajal believed that through “enhanced assimilation,” new patterns of connections could spawn as well as stronger connections being made (Berlucchi & Buchtel, 2009, p.312). This theory, although not fully realized until the work of Hebb, definitely changed the entire discipline of psychology.
Not everyone has been in agreement on the notion of neural plasticity however. Meyer believed that psychologist were attempting to throw into the brain some sort of psychological power rather than attempting to explain it through strictly physical means (Berlucchi & Buctel, 2009). One of the chief opponents of the theory of neural plasticity came from someone we already know, Karl Lashley (Berlucchi & Buchtel, 2009). “His attack on the theory was based on two kinds of evidence: (1) a learned response could be performed by means of neural paths that had never been used during the learning process and were completely separated from the trained path; (2) in higher animals and especially in humans there are many instances of temporary associations or one-trial learning, which by definition do not require any repetition of stimuli and responses” (Berlucchi & Buchtel, 2009, p.315).
He performed an experiment in which he paralyzed the motor cortex responsible for one of the arms of a monkey and then had the monkey learn a task with the other arm (Berlucchi & Buchtel, 2009). When the monkey had recovered somewhat of his ability to use the hand that had been previously paralyzed, he paralyzed the other one in the same manner and found that the monkey could do the same task it was asked to do before with the previously paralyzed arm (Berlucchi & Buchtel, 2009). He found that the monkey could perform this task successfully and in his mind this meant that since those neurons of the arm that was first paralyzed never had those neurons habituate the task but still managed to learn the task went against the concept of neural plasticity (Berlucchi & Buchtel, 2009). Herrick answered Lashley’s assumed answer to learning by suggesting that the studies having to do with split-brain patients shows that information that is learned is shared with both sides of the brain and therefore his supposed refutation of this theory was invalid (Berlucchi & Buchtel, 2009). Although not everyone agreed, it has come to be known as one of the definitive theories of neuroscience today.
Hebb, although he did not wish to take credit because of the work by Tanzi, is credited with coming up with a theory regarding neural plasticity in 1949 (Berlucchi & Buchtel, 2009). His theory, most widely known as Hebbian Synapses, basically says that change in a neuron is caused by multiple and simultaneous firings (Berlucchi & Buchtel, 2009). Allowing mental process to be explainable by physical means opened the door for Cognitive Neuroscience to flourish (Cowan, Harter, & Kandel, 2000). Neural plasticity has been both beneficial to the understanding of neurons and learning as a function of neuron maps (Posner & DiGirolamo, 2000). Studies on the activation of neurons has shown that there is a reduction of firing when a learned task is repeated where as firing is increased when a new task is performed (Posner & DiGirolamo, 2000).
This video is an example of how neural plasticity is implemented today (luju0002, 2007).
Research has shown that individuals with brain damage can learn new tasks as well as learn old tasks once learned (Robertson & Murre, 1999). It is likely however that these task learning abilities appear to look as though the person is back to normal functioning, but there can be many instances in which the learning is not the same as was or that a different type of functioning is occuring (Robertson & Murre, 1999). It has been shown that there is regrowth in areas thought to be previously lost due to lesions when normal activity in these areas is induced (Robertson & Murre, 1999). Hebbian theory supports these notions because it assumes that connections can reform if those neurons are fired at the same time for an extended period of time, just the same way learning occurs (Robertson & Murre, 1999). Thinking of it this way, we can see how the brain can be thought of as a muscle.
Studies were performed on animals in which motor tasks were taught (Robertson & Murre, 1999). After the parts of the brain responsible for that task were removed, functioning was still able to occur after retraining the task using other areas of the brain (Robertson & Murre, 1999).
Roberston & Murre (1999) look to von Monakow’s theory of diaschisis to explain the reasons for why people seem to have area’s which are not damaged but are also not functional.
Berlucchi, G. (2002). The origin of the term plasticity in the neurosciences: Ernesto Lugaro and chemical synaptic transmission. Journal of the History of the Neurosciences, 11(3), 305 – 309. doi: 10.1076/jhin.11.3.305.10396
Berlucchi, G. & Buchtel, H.A. (2009). Neuronal plasticity: Historical roots and evolution of meaning. Experimental Brain Research, 192(3), 307 – 319. doi: 10.1007/s00221-008-1611-6
Cowan, W.M., Harter, D.H. & Kandel, E.R. (2000). The emergence of modern neuroscience: Some implications for neurology and psychiatry. Annual Review of Neuroscience, 23, 343 – 391. doi: 10.1146/annurev.neuro.23.1.343
Hljod.Huskona (2008, February 26). Neurons in the brain – illustrations [Image File]. Retrieved from: http://www.flickr.com/photos/lorelei-ranveig/2294885420/
James, W. (1890). The principles of psychology. Retrieved from: http://psychclassics.yorku.ca/James/Principles/prin16.htm
luju0002 (2007, January 18). Brain plasticity [Video file]. Retrieved from: http://www.youtube.com/watch?v=TSu9HGnlMV0
Posner, M.I. & DiGirolamo, G.J.(2000). Cognitive neuroscience: Origins and promise. Psychological Bulletin, 126(6), 873 – 889. doi: 10.I037//0033-2909.126.6.873
Robertson, I.H., & Murre, J.M.J. (1999). Rehabilitation of brain damage: Brain plasticity and principles of guided recovery. Psychological Bulletin, 125(5), 544 – 574. Retrieved from: http://psycnet.apa.org.ezproxy.umw.edu:2048/journals/bul/125/5/544.pdf
By Travis Bice